The present invention relates to a testing circuit for a charge detection circuit, an LSI, an image sensor, and a testing method for the charge detection circuit for conducting a testing for checking operations of the charge detection circuit which is provided in devices such as image sensor including an X-ray sensor.
Conventionally, an X-ray capturing apparatus using films has been widely used as an X-ray medical diagnostic apparatus. However, in recent years, a flat-type X-ray sensor for obtaining image data has been developed in which a photoelectric conversion layer for converting X-rays to charges is provided on a TFT array substrate used in a liquid crystal display device, and it has been close to practical use as an X-ray capturing apparatus.
A schematic arrangement of a conventional, typical image sensor having two-dimensional matrix structure is the same as that as shown in FIG. 2, which is used for description of the embodiments.
More specifically, an image sensor 48 is arranged as shown in FIG. 2 in such a manner that a glass substrate 50 has a photoelectric conversion layer 54 and a bias electrode 52 thereon. On the surface of the photoelectric conversion layer 54 of the glass substrate 50, pixel electrodes 56 aligned in a matrix manner, storage capacitors (pixel capacitors) 17, switching elements 18, scanning lines (row) 10, and data lines (column) 12 are provided. The scanning lines 10 and the data lines 12 are connected to a scan drive unit (gate driver) 14 and a reading circuit (charge detection circuit) 16, respectively.
Thus, the image sensor 48 includes a photoelectric converting section, which is mainly composed of the photoelectric conversion layer 54 and the storage capacitor 17, for converting photons such as X-rays into charges and storing the charges, and the reading circuit 16 for reading signals of charges supplied from the photoelectric converting section.
Here, the following will describe a testing method for checking whether or not a large number of reading circuits 16 integrated into an LSI shown in FIG. 2 operate normally.
In case where a charge supply circuit 100 for carrying out a testing is connected to an input terminal of the LSI including a CSA 20, a circuit diagram is such a circuit diagram as shown in FIG. 12.
In this circuit diagram, in case where TC2 is turned OFF and TC1 is turned ON, a charge Vinxc3x97CT is stored in a capacitor CT.
On the other hand, in case where TC1 is turned OFF and TC2 is turned ON, the charge Vinxc3x97CT is supplied to the CSA 20. At this point, an output of the CSA 20 becomes voltage of xe2x88x92Vinxc3x97CT/Cf, which is eventually outputted as digital data, with respect to Vref.
In the conventional testing method using a charge supply circuit 100, it is possible to check whether the reading circuit operates normally or not by observation of this outputted data. Also, in this testing method, voltage Vin supplied to the charge supply circuit 100 can be varied to the several levels of voltages so as to vary the amount of charges supplied to the CSA 20, so that it is possible to carry out more detailed testing.
Usually, a large number of reading circuits 16 as described above is integrated and incorporated into the LSI. With this, the testing for checking the operations of all reading circuits 16 in the LSI is carried out in such a manner that a probe is provided to the end part of the charge supply circuit 100 shown in FIG. 12, and the probe is sequentially contacted to each terminal of the reading circuit 16. Further, in order to improve the efficiency of measurement, a widely used method is that a testing apparatus having a plurality of charge supply circuits 100 and probes is arranged so that tests for the reading circuits 16 connected to a plurality of terminals are carried out simultaneously.
The above conventional testing method enables the testing relatively easily. However, because the charge supply circuit 100 must be connected to each of the large number of reading circuits 16 integrated so that the testing is carried out by voltage application, the method provides the extreme inefficiency of the measurement. Also, in case where the testing is carried out with respect to a plurality of reading circuits 16 at one time of measurement as described above, conditions such as length of lines differs depending on the difference in physical position of each charge supply circuit. This increases the influence in variation of parasitic capacitance, which causes a difficulty of a highly accurate testing.
In case of the actual testing with respect to the input range of 100 points, prepared are 100 types of input voltages, 100 types of capacitances CT, 100 types of combinations between the input voltage Vin and the capacitance CT, or others.
However, this also arises a problem that such a testing method causes an overload on the charge supply circuits 100, so that it is impossible to carry out an accurate testing for checking the reading circuit 16""s operation.
An object of the present invention is to provide a testing circuit for the charge detection circuit, an LSI, an image sensor, and a testing method for the charge detection circuit, which can accurately carry out a testing for checking operations of the charge detection circuit which requires an extremely accurate detection of charges as that of an X-ray sensor.
In order to achieve the above object, the testing circuit for the charge detection circuit of the present invention, which observes a signal outputted from the charge detection circuit in response to a signal waveform supplied from voltage applying means so as to check whether or not the charge detection circuit operates normally, the testing circuit comprising:
a capacitor for causing the charge detection circuit to serve as a reverse amplifier circuit with respect to voltage input; and
switching means for providing the capacitor between an output terminal of the voltage applying means and the charge detection circuit when the charge detection circuit is tested, and for not providing the capacitor when the charge detection circuit regularly operates.
According to the above arrangement, the switching means can switch a testing mode for checking operations and a regular operation mode of the charge detection circuit by not inserting the capacitor in case where the charge detection circuit operates regularly and by inserting the capacitor in case where the testing for checking operations is carried out with respect to the charge detection circuit. Also, it is possible to easily carry out the testing for checking operations of the charge detection circuit.
More specifically, the testing circuit for the charge detection circuit according to the present invention is provided with the capacitor for causing the charge detection circuit to operate as a voltage input circuit, and the switching means for determining whether the capacitor is inserted or not.
With this arrangement, the charge detection circuit can conduct regular operations with the testing circuit provided by deleting (causing not to operate) the capacitor in the regular operation and by inserting the capacitor in the testing for checking operations of the charge detection circuit.
More specifically, in case where the testing for the charge detection circuit is carried out, the capacitor is inserted so that the capacitor and the charge detection circuit can serve as a reverse amplifier circuit. It is possible to easily carry out the testing for checking operations of the charge detection circuit by comparing and observing between the signal waveform applied to the input terminal and the signal waveform outputted.
Further, according to the testing circuit for the charge detection circuit of the present invention, the switching means can switch the regular operation mode and the testing mode for checking operations of the charge detection circuit only by deleting (causing not to operate) or inserting the capacitor, so that the testing circuit for the charge detection circuit can be provided inside devices such as an LSI. Therefore, it is not necessary to connect the conventional charge supply circuit to the input section of the charge detection circuit for the charge supply to the charge detection circuit in the testing for checking operations of the charge detection circuit. This makes it possible to efficiently carry out the testing for checking operations of the charge detection circuit only by supplying the signal waveform to the input terminal.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.